This invention relates to the flow management of concentrically flowing annular fluid streams. More particularly, this invention relates to apparatus operable to invert the flow pattern of two concentric annular flow streams and operable to combine the two flow streams for discharge as a single annular flow stream.
It is sometimes necessary or desirable to invert the flow pattern formed by two fluid streams that flow through concentrically arranged annular flow ducts such that the fluid stream originally occupying the innermost annular portion of the flow pattern concentrically surrounds the fluid stream that originally formed the outermost portion of the flow pattern. In some situations, designing apparatus for effecting such flow inversion is greatly complicated by various constraints.
For example, in U.S. Pat. Nos. 3,779,282 and 3,792,584, issued to Gary W. Klees and assigned to the assignee of this invention, flow inversion apparatus is disclosed which can be utilized within gas turbine engines for directing and managing various coaxially flowing annular fluid streams such as those routed to or from the fan and compressor stages of the gas turbine engine, auxiliary air intakes, and exhaust nozzles. As is disclosed in the aforementioned patents, and is recognized within the art, flow management within a gas turbine engine should preferably be accomplished within the space confines defined by the ducts which contain and direct the coaxially flowing fluid streams. Further, to prevent undesirable energy losses from occurring, the fluid passages necessary to invert the flow pattern must be smoothly contoured and exhibit a relatively constant cross-sectional area.
In the flow inversion arrangements disclosed in the Klees patents, a plurality of longitudinally extending thin-walled duct elements nest together to form an axially extending annular assemblage. The duct elements are contoured and arranged such that, with respect to the direction of fluid flow, the forward or entrance end of the assemblage forms two concentrically arranged annular openings wherein the forward ends of individual duct elements partition the annular openings into equal area annular sectors. Thus, as the two concentrically flowing fluid streams are received by such flow inversion arrangement, each of the fluid streams is divided into a plurality of separate flow streams with each of the flow streams being contained and directed by one of the duct elements.
To effect the desired "crossover" or flow inversion, the individual duct elements that form the center or inner annular entrance opening smoothly change in cross-sectional geometry while remaining of substantially constant cross-sectional area to gradually direct the centroid of the flow stream travelling therethrough outwardly toward the outer circumference of the annular envelope defined by the assemblage of duct elements. The duct elements that form the sectored outer annular entrance opening are shaped and contoured in essentially a complementary manner to those duct elements which receive the inner fluid stream to gradually direct the centroid of the flow streams passing therethrough inwardly toward the inner circumference of the annular envelope provided by the assemblage. In particular, the complementary contouring of the duct elements for receiving and subdividing each of the fluid streams causes the individual flow streams formed thereby to assume a flow pattern which is annular in geometry with the flow streams derived from each of the received annular fluid streams being circumferentially interspersed segments of the annular flow pattern.
With continued reference to the direction of fluid flow, the duct elements which contain and direct a portion of the fluid flow of the received outer annular flow stream then smoothly change in geometry while maintaining substantially constant cross-sectional area to move the centroid of the fluid streams flowing therethrough gradually inward. In a complementary manner, the duct elements which contain and direct portions of the received inner annular flow stream smoothly change in geometry while maintaining substantially constant cross-sectional area to direct the centroid of the fluid streams flowing therethrough gradually outward. In particular, the duct elements are configured and arranged such that concentric annular discharge openings are defined in the exit plane of the assemblage with each duct element forming a sector of either the inner or outer annular discharge opening. Since a duct element which receives a sectorial portion of the received inner annular flow stream forms a sector of the outer discharge annulus and a duct element which receives a sectorial portion of the received outer annular flow stream forms a sector of the inner discharge annulus, the desired flow inversion is effected. Since each duct element is of relatively constant cross-sectional area and smoothly changes in cross-sectional geometry, little or no energy losses occur. Further, because of the geometry of each duct element, the nested assemblage of duct elements effectively forms an extension of the annular flow ducts which originally contained and directed the fluid streams, i.e., the envelope of the flow inversion apparatus need not extend radially outward beyond the outer diameter of the ducts which contain and direct the original flow streams.
In situations in which the received coaxial flowing annular flow streams are to be selectively discharged in the original flow pattern or discharged with an inverted flow pattern, the flow inversion device of Klees is divided into an upstream and a downstream portion at the above-mentioned plane at which the flow streams of the two fluid streams occupy circumferentially interspersed segments of a single annular flow pattern. In such an embodiment of the Klees apparatus, which is necessarily limited to situations in which the cross-sectional area of the two received fluid streams are equal, n duct elements for directing a portion of the received inner annular flow stream and n duct elements for directing a portion of the received outer annular flow stream are employed with each of the duct elements being of equal area at every position along the length of the flow system. Switching between the previously described flow inversion configuration and a "straight through" flow configuration is effected in such an embodiment by rotating either the upstream or downstream portion of the flow inversion apparatus by an angle of .pi./n radians. Such an angular displacement causes duct elements of the downstream portion which are respectively aligned with duct elements of the upstream portion that receive the outer and inner fluid streams when the system is operated in the flow inversion mode to become respectively aligned with duct elements that receive the opposite one of the two received fluid streams.
Although a flow management system of the type disclosed by Klees is highly satisfactory in situations requiring flow inversion or selective operation in a flow inversion mode and a straight through flow mode, such a system is not applicable to other flow control situations. For example, in one type of gas turbine engine that is commonly referred to as a multicycle engine and used to propel aircraft, it is necessary not only to invert inner and outer concentric annular flow streams during certain operating modes of the engine, but also to combine the two flow streams for discharge as a single annular flow stream during other engine operating modes. More specifically, in this type of engine, the engine core delivers combustion products in an annular flow pattern that is coaxially surrounded by an annular fluid stream that is supplied through an annular flow duct by the engine fan stage. During certain modes of operation such as aircraft takeoff, climb and high speed (e.g., supersonic) cruise, the two fluid streams are inverted such that the flow provided by the fan stage drives an aft turbine stage and the combustion products supplied by the engine core flow through an annular duct that concentrically surrounds the aft turbine stage. During other modes of operation such as are employed in a flight regime commonly referred to as holding, and during supersonic cruise operation in which maximum thrust is not required, the flow provided by the fan stage and the combustion products provided by the engine core are combined to drive the aft turbine, and no fluid is exited through the annular flow duct that extends rearwardly about the aft turbine. As is known by those skilled in the art, the use of such a gas turbine engine, preferably with the selective burning of fuel in the region of the fan duct (i.e., "duct-burning"), provides an efficient, relatively low-noise engine which meets the various operational demands for engines that propel aircraft that operate in both subsonic and supersonic flight regimes.
A flow control system operable to invert a received concentric annular flow pattern and operable to combine the two received flow streams for discharge as a single annular flow stream can be subject to design constraints in addition to the previously noted volume and flow passage constraints. For example, in the above described multicycle gas turbine engine, the means employed within the flow control system to cause the selective flow inversion or discharge as a single, annular flow stream should not be structurally complex to thereby ensure that the flow control system is reliable and is relatively economical to fabricate and maintain. Further, because fluid supplied by the fan stage and the core generator are at a relatively high temperature, relatively high fluid pressure, and flow with considerable particle velocity, the mechanism for causing the selective flow inversion or single stream discharge should be arranged for operation by relatively low operative forces and be substantially unaffected by wide variations in temperature. Additionally, to provide essentially fail-safe operation, preferably such a flow control system should be arranged such that abrupt switching from one mode of operation to the other does not occur upon operational failure of the means for actuating the flow control system.
Accordingly, it is an object of this invention to provide a flow control system that is operable to invert two concentrically arranged annular fluid streams and is operable to discharge the two fluid streams as a single fluid stream of angular cross section geometry.
It is a further object of this invention to provide a flow control system of the above-described type wherein such flow control is effected within a specific volume having relatively low axial length and having an annular envelope of inner and outer diameter not substantially exceeding that of the flow ducts the supply the concentrically arranged fluid stream.
It is yet another object of this invention to provide a flow control system of the above-described type that is operable by relatively low actuation forces.
It is still another object of this invention to provide a flow control system of the above-described type for use in a gas turbine engine wherein failure of the system actuation device does not cause the flow control system to abruptly switch operational modes.